Topic: Horner's Syndrome
Subject: Medicine
A 66-year-old diabetic man presents with constriction of the pupil, drooping of the upper lid, and anhidrosis on the left. Which one of the following nerves is most likely involved?

This patient has symptoms of miosis (constriction of the pupil), partial ptosis (drooping of the upper lid) and loss of hemifacial sweating (anhidrosis). These are symptoms of Horner syndrome, which is caused by the interruption of the sympathetic nerve fibers. This can occur centrally (ie, between the hypothalamus and the fibers' point of exit from the spinal cord [C8 to T2]) or peripherally (ie, cervical sympathetic chain, superior cervical ganglion, along the carotid artery).